Modification of sPEEK Membranes

Another example of inorganic phase incorporation with the sPEEK polymeric matrix is constituted by the use of zeolite. Intaraprasit and Kongkachuichay [151] studied the incorporation of Analcime natural zeolite (10 wt%) in sPEEK, achieving a high proton conductivity of —4.0 X10 S/cm at 90 °C and 100% RH (Table 3.8). 

This result may be due to the protons inside the connected 3D channels of analcime, obtained after H-form transformation. Therefore, these protons act as bridges for the proton transport, thus increasing the proton conductivity. Furthermore, the incorporation of solid particles in the hybrid membrane increases the resistance to hydrogen diffusion through the membrane, lowering its fuel crossover in PEMFC applications. Nevertheless, at 7 90°C, the sPEEK/Analcime membrane loses water fast with a consequent depletion of proton conductivity [151]. 

7 sPEEK-WC and Its Derivative Sulfonated Polymers As well known, PEEK, PEEKK, and PEK are polymers having high degree of crystallinity and are insoluble in water and in most of the common organic solvents. The insolubility properties of the PEEK polymer may be overcome by a new type of polymer, the PEEK-WC, which is not classified as a blend, composite, or hybrid 

Other studies have been carried out for the preparation of modified sPEEK-WC membranes, for example, by incorporating 20 wt% amorphous zirconium sulfophenyl phosphonate (Zr/SPP) as a proton conductivity carrier in order to enhance the transport behaviors of the composite membranes (sPEEK-WC-Zr/SPP). Furthermore, the Zr(SPP)/SPEEK-WC membrane absorbs less water and methanol than the pristine sPEEK-WC membrane and methanol absorption does not increase significantly with temperature, contrary to the pristine sPEEK-WC membrane, particularly at high DS. Another benefit of the Zr/SPP incorporation is related to methanol permeability, which is lower than that of Nafion owing to its microstmcture with narrow and highly branched channels, which are responsible for the lower methanol crossover. Nevertheless, as demonstrated by Regina et al. [176], proton conductivity of these composite membranes is improved by Zr/SPP incorporation only at lower 

reaching a best value of 2.0x 10 S/cm at 80 °C and with a DS of 57% (Table 3.8). In another study, the embedding of HPAs in ehlorosulfonated PEEK-WC (sPEEK-WC/HPA) was also followed without achieving substantial improvements in proton conductivity of the eomposite membranes, although better than that of Nafion at T 100°C. Indeed, at around 100°C and 85% RH, sPEEK-WC/HPA shows a proton conductivity of 4.0x 10 S/cm, even if, eompared with the other results reported in Table 3.8, it appears similar to other sPEEK-WC-based membranes [207]. 

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